1. Field of Invention
The present invention relates to a sheet conveying stepping motor control method and apparatus for use in printers, facsimiles and the like.
2. Description of Related Art
There are known sheet conveying mechanisms for electronic appliances such as printers, facsimiles and the like, wherein a sheet conveying roller is driven by a stepping motor. In such electronic appliances, intermittent sheet conveyance is performed at various conveying speeds and amounts. For example, in a low-to-intermediate speed conveyance, the stepping motor is operated at a low-to-intermediate speed by self-start driving in order to avoid the motor operating out-of-step. In a high-speed conveyance, the stepping motor is operated at a high speed by performing step-up and step-down control. Furthermore, in a fractional conveyance, the stepping motor is operated a very small rotational angle at a time. In such various methods of intermittent conveyance according to the conventional art, the stepping motor is driven in a two-two phase excitation (magnetization) mode through constant-current control.
However, in the high-speed sheet conveyance performed in the two-two phase excitation mode by constant-current control, the operating speed of the motor considerably fluctuates at the motor starting and stopping points, thereby giving rise to a noise problem. Furthermore, such motor revolution speed fluctuation results in variations in the amount of conveyance, thereby degrading print quality and the like.
Furthermore, if the low-to-intermediate sheet conveyance in the two-two phase excitation mode is performed by self-start driving, the operating speed of the motor considerably fluctuates at the start and stop of the motor operation, thereby giving rise to a noise problem. Furthermore, due to such motor revolution speed fluctuation, the amount of conveyance varies.
In the fractional sheet conveyance performed in the two-two phase excitation mode, the stepping motor is frequently started and stopped, thereby producing vibrations that result in noise.